A positive electrode catalyst for metal-gas batteries, a method for producing the same, and use thereof

Abstract

The application discloses a positive electrode catalyst of a metal gas battery and a preparation method and application thereof, and belongs to the technical field of metal gas battery materials. The preparation method of the positive electrode catalyst of the metal gas battery comprises the following steps: dispersing graphene oxide in a first solvent to obtain a graphene oxide solution; adding melamine and formaldehyde into the graphene oxide solution to perform a hydrothermal reaction, so as to obtain a nitrogen-doped graphene oxide intermediate; performing pyrolysis treatment on the nitrogen-doped graphene oxide intermediate, so as to obtain three-dimensional nitrogen-doped graphene; dissolving inorganic iron salt, inorganic cobalt salt and sodium hydroxide in a second solvent, and then adding ethylenediamine, so as to obtain a mixed solution; dispersing the three-dimensional nitrogen-doped graphene in the mixed solution to perform a reaction, so as to obtain the positive electrode catalyst. The positive electrode catalyst is applied to an aluminum gas battery, and problems such as slow oxygen reduction / precipitation kinetics in an aluminum-air battery and low nitrogen reduction reaction efficiency in an aluminum-nitrogen gas battery can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal gas battery materials, and particularly relates to a positive electrode catalyst of a metal gas battery and a preparation method and application thereof. BACKGROUND

[0002] With the increasing global energy demand, the consumption of traditional fossil fuels has brought double pressures of environmental pollution and resource depletion. Under this background, it is crucial to develop efficient and sustainable energy storage and conversion technologies. Metal-air batteries and metal-nitrogen batteries, as the next generation of energy systems, have attracted much attention due to their unique advantages. Among them, aluminum-air batteries are considered as a promising energy solution due to their extremely high theoretical energy density, abundant aluminum resources in the earth's crust, low cost, and inherent safety.

[0003] However, despite the promising prospects, the commercial application of aluminum-air batteries still faces many severe technical challenges. The most core problem is the slow kinetics of the oxygen reduction / evolution reaction (ORR / OER) at the air cathode, which directly leads to low power density and overall efficiency of the battery. In addition, the poor stability of the positive electrode catalyst is also a key problem, which affects the cycle life of the battery. In addition to the cathode problem, the aluminum anode is prone to self-corrosion and hydrogen evolution in aqueous electrolytes, and may form a passivation layer, which will reduce the effective volume energy density and storage life of the anode. In order to overcome these challenges, electrocatalysts play a crucial role in aluminum-air batteries. In the prior art, although noble metal catalysts such as platinum (Pt) and iridium dioxide (IrO2) have excellent activity, their high cost and scarcity seriously hinder large-scale commercial application.

[0004] In addition, aluminum-nitrogen batteries represent a forward-looking new type of battery system, which uniquely combines energy storage with electrochemical nitrogen reduction reaction (NRR), thereby enabling simultaneous synthesis of ammonia from atmospheric nitrogen (N2). This method provides a promising, environmentally friendly and sustainable alternative to the traditional energy-intensive Haber-Bosch process. Although aluminum-nitrogen batteries have great potential, NRR itself faces severe challenges, mainly manifested as low ammonia yield and low faradic efficiency. This is mainly due to the high bond energy of N≡N triple bond, and the strong competition with hydrogen evolution reaction (HER), which has a similar equilibrium potential as NRR in acidic and alkaline conditions. In addition, the instability of the cathode electrocatalyst also leads to a significant decline in overall performance.

[0005] In summary, current aluminum gas battery technologies, including aluminum-air batteries and emerging aluminum-nitrogen batteries, still face numerous challenges in practical applications. Existing research mainly focuses on the improvement of catalyst materials, electrolyte engineering, and electrode structure design. However, these efforts have not completely solved the key bottlenecks of efficiency, stability, cost, and sustainability that aluminum gas batteries face in practical applications. In particular, a positive electrode catalyst that can simultaneously exhibit excellent performance, high stability, and cost-effectiveness in ORR / OER and NRR is still a technical problem that needs to be broken through in this field.

[0006] Therefore, whether it is an aluminum-air battery or an aluminum-nitrogen battery, the demand for high-performance catalysts is urgent, but existing high-performance catalysts are mostly noble metals, which are costly and unsustainable, limiting their widespread application. SUMMARY

[0007] The purpose of the present application is to provide a preparation method of a metal gas battery positive electrode catalyst to solve the problems raised in the background art.

[0008] To achieve the above-mentioned purpose, the embodiments of the present application provide the following technical solutions:

[0009] A preparation method of a metal gas battery positive electrode catalyst, comprising the following steps:

[0010] Disperse graphene oxide in a first solvent to obtain a graphene oxide solution;

[0011] Add melamine and formaldehyde to the graphene oxide solution for hydrothermal reaction to obtain a nitrogen-doped graphene oxide intermediate;

[0012] Pyrolysis treat the nitrogen-doped graphene oxide intermediate to obtain three-dimensional nitrogen-doped graphene;

[0013] Dissolve inorganic iron salt, inorganic cobalt salt, and sodium hydroxide in a second solvent, and then add ethylenediamine to obtain a mixed solution;

[0014] Disperse the three-dimensional nitrogen-doped graphene in the mixed solution and react at a temperature of 105-115°C to obtain a positive electrode catalyst.

[0015] Further, the mass ratio of the graphene oxide to the melamine is (0.1-0.3):(0.4-0.6); the mass-volume ratio of the graphene oxide to the first solvent is (0.1-0.3) g:30 mL; and the volume ratio of the formaldehyde to the first solvent is (1-1.5):30.

[0016] Further, the temperature of the hydrothermal reaction is 170-190°C.

[0017] Further, the pyrolysis treatment temperature is 750-850℃.

[0018] Further, the molar ratio of the inorganic iron salt, the inorganic cobalt salt and sodium hydroxide is (2-4):(1-2):(12-18); the molar volume ratio of the inorganic iron salt to the second solvent is (2-4) mol:7 mL; the volume ratio of the ethylenediamine to the second solvent is (1.5-2.5):1; the mass volume ratio of the three-dimensional nitrogen-doped graphene to the second solvent is (0.01-0.1):7 mL.

[0019] Another object of the embodiments of the present application is to provide a positive electrode catalyst prepared by the above preparation method.

[0020] Another object of the embodiments of the present application is to provide an application of the above positive electrode catalyst in preparing a metal gas battery.

[0021] Further, the metal gas battery is an aluminum gas battery.

[0022] Another object of the embodiments of the present application is to provide a metal gas battery comprising a negative electrode, an electrolyte and the above positive electrode catalyst.

[0023] Further, the negative electrode is aluminum; the electrolyte is an ionic liquid of aluminum chloride and 1-ethyl-3-methylimidazolium chloride; and the positive electrode catalyst is coated on a carbon cloth.

[0024] The preparation method of the positive electrode catalyst of the metal gas battery provided by the present application introduces three-dimensional nitrogen-doped graphene to load cobalt ferrite, so that cobalt ferrite nanoparticles are uniformly dispersed on the wrinkled surface of the three-dimensional nitrogen-doped graphene, effectively preventing particle agglomeration and maximizing the exposure of active sites. Moreover, the close combination and synergistic interaction between the three-dimensional nitrogen-doped graphene and cobalt ferrite further optimize the electron transport kinetics and active site accessibility, thereby bringing excellent bifunctional ORR / OER catalytic activity and promising NRR performance. When the positive electrode catalyst is applied to an aluminum gas battery, it can solve the problems of slow oxygen reduction / oxidation kinetics in aluminum-air batteries and low nitrogen reduction reaction efficiency in aluminum-nitrogen batteries, effectively solve the core problems in existing aluminum gas battery technology, and thus promote the commercialization process. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 XRD patterns of CoFe2O4 / N-rGO prepared in Example 1, N-rGO prepared in Comparative Example 1 and CoFe2O4 prepared in Comparative Example 2.

[0026] Figure 2Raman spectra of CoFe2O4 / N-rGO prepared in Example 1, N-rGO prepared in Comparative Example 1, and CoFe2O4 prepared in Comparative Example 2.

[0027] Figure 3 SEM images of CoFe2O4 / N-rGO prepared in Example 1 and N-rGO prepared in Comparative Example 1.

[0028] Figure 4 Performance chart of an aluminum-air battery provided in an embodiment of the present application.

[0029] Figure 5 Performance chart of an aluminum-nitrogen battery provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0031] In one embodiment of the present application, a preparation method of a positive electrode catalyst of a metal-gas battery is provided, comprising the following steps:

[0032] S1, dispersing 0.1-0.3 g of graphene oxide (GO) in 30 mL of a first solvent to obtain a graphene oxide solution;

[0033] S2, adding 0.4-0.6 g of melamine and 1-1.5 mL of formaldehyde to the graphene oxide solution, heating to 170-190 ℃ for reaction to obtain a nitrogen-doped graphene oxide intermediate;

[0034] S3, after washing and drying the nitrogen-doped graphene oxide intermediate, pyrolysis treatment is performed under a nitrogen atmosphere at a temperature of 750-850 ℃ to obtain three-dimensional nitrogen-doped graphene (N-rGO);

[0035] S4, dissolving 2-4 mmol of an inorganic iron salt, 1-2 mmol of an inorganic cobalt salt, and 12-18 mmol of sodium hydroxide in 7 mL of a second solvent, and then adding 10.5-17.5 mL of ethylenediamine to obtain a mixed solution;

[0036] S5, dispersing 0.01-0.1 g of three-dimensional nitrogen-doped graphene in the above mixed solution, and performing reaction at a temperature of 105-115 ℃ to obtain three-dimensional nitrogen-doped graphene loaded with cobalt ferrite (CoFe2O4 / N-rGO), which is the positive electrode catalyst.

[0037] It should be noted that the first solvent and the second solvent described above can be deionized water, but are not limited thereto. The inorganic iron salt described above can be selected from, but is not limited to, iron chloride and iron nitrate, and is preferably FeCl3·6H2O. The inorganic cobalt salt described above can be selected from, but is not limited to, cobalt chloride and cobalt nitrate, and is preferably CoCl2·6H2O.

[0038] In another embodiment of the present application, a metal gas battery is also provided, comprising a negative electrode, an electrolyte, and the positive electrode catalyst described above.

[0039] Specifically, the metal gas battery is an aluminum-air battery or an aluminum-nitrogen battery; a CR2025 button cell can be used, and the positive electrode shell has a hole. The aluminum-air battery or the aluminum-nitrogen battery is mainly composed of the following key components:

[0040] 1. Negative electrode: aluminum sheet; pure aluminum sheet is used as the negative electrode material. Aluminum has a very high theoretical specific capacity (2980 mAh / g) and volume capacity (8046 mAh / cm 3 ), and is low in cost, abundant in reserves, non-toxic, and safe; during the discharge process, the aluminum sheet undergoes oxidation reaction and releases electrons.

[0041] 2. Electrolyte: an ionic liquid of aluminum chloride and 1-ethyl-3-methylimidazolium chloride, which is an ionic liquid formed by mixing anhydrous aluminum chloride (AlCl3) and 1-ethyl-3-methylimidazolium chloride (EMIC) at a molar ratio of (1-1.5):1; this non-aqueous ionic liquid electrolyte has high ionic conductivity, is not flammable, has a wide electrochemical window, and has good stability. In the AlCl3 / EMIC system, Al2Cl7 - anions act as the main charge carriers, promoting aluminum deposition / dissolution and ensuring the charge / discharge process of the battery.

[0042] 3. Carbon cloth coated with a positive electrode catalyst (CoFe2O4 / N-rGO); the uniform dispersion of CoFe2O4 nanoparticles on the N-rGO wrinkle surface effectively prevents particle agglomeration and maximizes the exposure of active sites. The close combination and synergistic interaction between N-rGO and CoFe2O4 further optimize the electron transport kinetics and active site accessibility, resulting in excellent bifunctional ORR / OER catalytic activity and promising NRR performance. The three-dimensional hierarchical porous structure of the positive electrode catalyst (CoFe2O4 / N-rGO) ensures that the reactants can be seamlessly distributed to the active sites, which is crucial for the sustained high performance of the battery positive electrode.

[0043] The aluminum gas battery provided in the embodiments of the present application, whether as an aluminum-air battery or an aluminum-nitrogen battery, has a working process based on the high-efficiency catalysis of the positive electrode catalyst CoFe2O4 / N-rGO in specific electrochemical reactions.

[0044] wherein, as an aluminum-air battery, the discharge process is: the aluminum negative electrode undergoes an oxidation reaction (Al→ Al 3+ +3e - ). Meanwhile, under the action of the positive electrode catalyst CoFe2O4 / N-rGO, oxygen in the air undergoes ORR, consumes electrons and combines with ions in the electrolyte. The high ORR activity and stability of the positive electrode catalyst CoFe2O4 / N-rGO ensure high energy output and long cycle life. The charging process is: under the action of an external power source, the reaction proceeds in reverse, the positive electrode catalyst CoFe2O4 / N-rGO promotes OER, regenerates oxygen, and at the same time the aluminum negative electrode undergoes a reduction reaction.

[0045] As an aluminum-nitrogen battery, the discharge process is: the aluminum negative electrode undergoes an oxidation reaction. Under the action of the positive electrode catalyst CoFe2O4 / N-rGO, N2 undergoes electrochemical NRR to generate aluminum nitride (AlN), while releasing electrical energy. The positive electrode catalyst CoFe2O4 / N-rGO significantly enhances the adsorption and activation of N2, improves the ammonia yield and Faraday efficiency, and the ionic liquid electrolyte effectively suppresses the competitive hydrogen evolution reaction. The charging process is: under the action of an external bias, the AlN in the cathode decomposes back into metal ions and gaseous nitrogen, thereby realizing chargeability.

[0046] The embodiment of the present application provides a high-performance, multifunctional and cost-effective positive electrode catalyst for aluminum gas batteries through the above detailed technical solutions, which provides an innovative approach to solving the key challenges in the current energy storage and green chemical synthesis fields. The embodiment of the present application can overcome the shortcomings of existing aluminum gas battery technology, and by introducing CoFe2O4 / N-rGO as a positive electrode catalyst, the following purposes can be achieved:

[0047] 1. Significantly improve the performance of aluminum-air batteries. Solve the problems of slow ORR / OER kinetics and poor positive electrode stability, and provide a high-efficiency and high-stability non-noble metal alternative.

[0048] 2. Improve the efficiency and selectivity of aluminum-nitrogen batteries. Overcome the challenges of low ammonia yield and low Faraday efficiency in NRR, effectively suppress the competitive hydrogen evolution reaction, and ensure the long-term stability of the catalyst.

[0049] 3. Achieve cost-effectiveness and sustainability. Provide a high-performance positive electrode catalyst based on abundant and low-cost materials, thereby promoting the commercialization and sustainable development of aluminum gas battery technology.

[0050] The following examples are some specific implementation cases of the present application in actual application, but are not limited thereto.

[0051] Example 1: The embodiment provides a preparation method of a positive electrode catalyst of a metal-gas battery, comprising the following steps:

[0052] S1, 0.2g of graphene oxide is dispersed in 30ml of deionized water, and a uniform graphene oxide solution is obtained by ultrasonic dispersion treatment for 1 hour;

[0053] S2, 0.5g of melamine and 1.2ml of formaldehyde are added to the above graphene oxide solution under stirring, and then transferred to a polytetrafluoroethylene lined autoclave, heated to 180°C for reaction for 10 hours to obtain a nitrogen-doped graphene oxide intermediate;

[0054] S3, the nitrogen-doped graphene oxide intermediate is washed with deionized water and dried in an 80°C oven, and then heated to 800°C under a nitrogen atmosphere for pyrolysis treatment for 3 hours to obtain three-dimensional nitrogen-doped graphene (N-rGO);

[0055] S4, 3mmol of FeCl3·6H2O, 1.5mmol of CoCl2·6H2O and 15mmol of sodium hydroxide are dissolved in 7ml of deionized water, stirred uniformly at room temperature, and then 14ml of ethylenediamine is slowly added to obtain a mixed solution;

[0056] S5, 0.05g of three-dimensional nitrogen-doped graphene is dispersed in the above mixed solution, and the black solution is formed by continuous stirring for 30 minutes, and then transferred to a polytetrafluoroethylene lined autoclave, reacted at 110°C for 15 hours, and then cooled to room temperature, and the precipitate is centrifuged, washed and vacuum dried to obtain three-dimensional nitrogen-doped graphene loaded cobalt ferrite (CoFe2O4 / N-rGO) as a positive electrode catalyst.

[0057] Example 2: The embodiment provides a preparation method of a positive electrode catalyst of a metal-gas battery, comprising the following steps:

[0058] S1, 0.1g of graphene oxide is dispersed in 30ml of deionized water, and a uniform graphene oxide solution is obtained by ultrasonic dispersion treatment for 1 hour;

[0059] S2, 0.4g of melamine and 1ml of formaldehyde are added to the above graphene oxide solution under stirring, and then transferred to a polytetrafluoroethylene lined autoclave, heated to 170°C for reaction for 10 hours to obtain a nitrogen-doped graphene oxide intermediate;

[0060] S3, the nitrogen-doped graphene oxide intermediate is washed with deionized water and dried in an 80°C oven, and then heated to 750°C under a nitrogen atmosphere for pyrolysis treatment for 3 hours to obtain three-dimensional nitrogen-doped graphene (N-rGO);

[0061] S4, 2 mmol of FeCl3-6H2O, 1 mmol of CoCl2-6H2O and 12 mmol of sodium hydroxide were dissolved in 7 mL of deionized water, stirred uniformly at room temperature, and then 10.5 mL of ethylenediamine was slowly added to obtain a mixed solution;

[0062] S5, 0.1 g of three-dimensional nitrogen-doped graphene was dispersed in the above mixed solution, and stirred for 30 minutes to form a black solution, which was then transferred to a polytetrafluoroethylene-lined autoclave and reacted at 105°C for 15 hours. After cooling to room temperature, the precipitate was centrifuged, washed and vacuum dried to obtain three-dimensional nitrogen-doped graphene loaded cobalt ferrite (CoFe2O4 / N-rGO) as a positive electrode catalyst.

[0063] Example 3: The example provides a preparation method of a positive electrode catalyst of a metal-gas battery, comprising the following steps:

[0064] S1, 0.3 g of graphene oxide was dispersed in 30 mL of deionized water, and uniformly dispersed by ultrasonic treatment for 1 hour to obtain a graphene oxide solution;

[0065] S2, 0.6 g of melamine and 1.5 mL of formaldehyde were added to the above graphene oxide solution under stirring, and then transferred to a polytetrafluoroethylene-lined autoclave and heated to 190°C for 10 hours to obtain a nitrogen-doped graphene oxide intermediate;

[0066] S3, the nitrogen-doped graphene oxide intermediate was washed with deionized water and dried in an 80°C oven, and then pyrolyzed at 850°C for 3 hours under a nitrogen atmosphere to obtain three-dimensional nitrogen-doped graphene (N-rGO);

[0067] S4, 4 mmol of FeCl3-6H2O, 2 mmol of CoCl2-6H2O and 18 mmol of sodium hydroxide were dissolved in 7 mL of deionized water, stirred uniformly at room temperature, and then 17.5 mL of ethylenediamine was slowly added to obtain a mixed solution;

[0068] S5, 0.01 g of three-dimensional nitrogen-doped graphene was dispersed in the above mixed solution, and stirred for 30 minutes to form a black solution, which was then transferred to a polytetrafluoroethylene-lined autoclave and reacted at 115°C for 15 hours. After cooling to room temperature, the precipitate was centrifuged, washed and vacuum dried to obtain three-dimensional nitrogen-doped graphene loaded cobalt ferrite (CoFe2O4 / N-rGO) as a positive electrode catalyst.

[0069] Comparative Example 1: The comparative example provides a preparation method of three-dimensional nitrogen-doped graphene (N-rGO), which is the same as Example 1, and specifically comprising the following steps:

[0070] S1, 0.2 g of graphene oxide was dispersed in 30 mL of deionized water, and a uniform graphene oxide solution was obtained by ultrasonic dispersion treatment for 1 hour;

[0071] S2, 0.5 g of melamine and 1.2 mL of formaldehyde were added to the above graphene oxide solution under stirring, and then transferred to a polytetrafluoroethylene-lined autoclave, heated to 180°C for reaction for 10 hours to obtain a nitrogen-doped graphene oxide intermediate;

[0072] S3, the nitrogen-doped graphene oxide intermediate was washed with deionized water and dried in an 80°C oven, and then pyrolysis treatment was carried out at 800°C for 3 hours under a nitrogen atmosphere to obtain three-dimensional nitrogen-doped graphene (N-rGO).

[0073] Comparative Example 2: The comparative example provides a preparation method of cobalt ferrite (CoFe2O4), which specifically comprises the following: 3 mmol of FeCl3·6H2O, 1.5 mmol of CoCl2·6H2O and 15 mmol of sodium hydroxide were dissolved in 7 mL of deionized water, stirred uniformly at room temperature, and then 14 mL of ethylenediamine was slowly added to obtain a mixed solution; the above mixed solution was transferred to a polytetrafluoroethylene-lined autoclave, reacted at 110°C for 15 hours, and then cooled to room temperature, and the product was centrifuged, washed and vacuum dried to obtain cobalt ferrite (CoFe2O4).

[0074] I. Structure, composition and morphology characterization: CoFe2O4 / N-rGO prepared in Example 1, N-rGO prepared in Comparative Example 1 and CoFe2O4 prepared in Comparative Example 2 were subjected to XRD pattern detection, and compared with the standard PDF card (PDF #03-0864) of CoFe2O4, and the results were as follows: Figure 1The XRD pattern of N-rGO shows a broad diffraction peak at about 26°, which is a typical characteristic peak of reduced graphene oxide (rGO), indicating that it has a graphitized structure but with a certain degree of disorder. The XRD pattern of CoFe2O4 shows multiple sharp and clear diffraction peaks, the positions of which are completely consistent with the characteristic peaks in the standard PDF card of CoFe2O4. The main diffraction peaks are located at about 30.2°, 35.6°, 43.5°, 57.2° and 62.8°, corresponding to the (220), (311), (400), (511) and (440) crystal planes of the spinel structure of CoFe2O4, respectively. This confirms that the synthesized CoFe2O4 nanocrystals have high crystallinity and pure spinel phase. The XRD pattern of CoFe2O4 / N-rGO composite shows both the broad diffraction peak of N-rGO and the sharp characteristic peaks of CoFe2O4. This clearly indicates that the CoFe2O4 nanocrystals have been successfully loaded and combined on the N-rGO substrate, and the crystal structures of the two components have been well maintained during the composite process.

[0075] The Raman spectra of graphene oxide (GO), CoFe2O4 / N-rGO prepared in Example 1, N-rGO prepared in Comparative Example 1, and CoFe2O4 prepared in Comparative Example 2 were detected, and the results are shown in Figure 2 The Raman spectrum of GO shows two typical characteristic peaks: D peak (about 1350 cm -1 ) and G peak (about 1580 cm -1 ); the D peak is related to defects and disordered structures in carbon materials, while the G peak represents the in-plane stretching vibration of sp2 hybridized carbon atoms. The Raman spectrum of N-rGO also shows D peak and G peak, and the intensity ratio (I D / I G ) of D peak and G peak changes, which reflects the defects and structural changes introduced during the reduction and nitrogen doping of graphene oxide. The Raman spectrum of CoFe2O4 shows the characteristic vibration mode of cobalt ferrite, which usually appears in the lower wave number region (such as about 600-700 cm -1 ), corresponding to the vibration of metal-oxygen bond. The Raman spectrum of CoFe2O4 / N-rGO shows the D peak and G peak of N-rGO and the characteristic peaks of CoFe2O4 superimposed. This further confirms the successful combination of CoFe2O4 and N-rGO, and the structural integrity of both components is retained in the composite material.

[0076] The SEM images of CoFe2O4 / N-rGO prepared in Example 1 and N-rGO prepared in Comparative Example 1 were detected, and the results are shown in Figure 3The SEM images of N-rGO show that the N-rGO presents obvious wrinkle, sheet structure, and cross-linking to form a porous three-dimensional network; this unique morphology is a typical feature of three-dimensional graphene materials, which provides a large specific surface area and an open pore structure. The SEM images of CoFe2O4 / N-rGO show that the CoFe2O4 nanoparticles are uniformly distributed and anchored on the wrinkle sheet surface of N-rGO; this uniform dispersion effectively prevents the agglomeration of CoFe2O4 nanoparticles, maximally exposes the active sites; at the same time, the CoFe2O4 / N-rGO as a whole still maintains the three-dimensional porous network structure of N-rGO, which is crucial for promoting the mass transfer and diffusion of reactants (such as O2 and N2).

[0077] In summary, the characterization results of XRD, Raman spectrum and SEM consistently prove that the CoFe2O4 / N-rGO positive electrode catalyst with high crystallinity CoFe2O4 nanocrystals and N-rGO closely compounded is successfully synthesized in the embodiments of the present application, and the unique structural characteristics lay a foundation for the subsequent excellent electrochemical performance in aluminum gas batteries.

[0078] II. Battery assembly and test: The battery performance test in the embodiments of the present application is based on a 2025 type button cell, and the electrode preparation, battery assembly and test process are as follows:

[0079] Electrode preparation: the positive electrode catalyst (CoFe2O4 / N-rGO prepared in Example 1 or N-rGO prepared in Comparative Example 1 or CoFe2O4 prepared in Comparative Example 2), Super P conductive additive and polyvinylidene fluoride (PVDF) are uniformly mixed in N-methyl pyrrolidone (NMP) solvent at a mass ratio of 80wt%:10wt%:10wt%, to prepare a slurry; the prepared slurry is sprayed on a circular carbon cloth to form a porous positive electrode; the coated carbon cloth is placed in a vacuum oven and dried at a temperature of 80°C for 12 hours to completely remove the residual solvent. The positive electrode catalyst load on each piece of carbon cloth is about 0.5 milligrams.

[0080] Battery assembly: the negative electrode adopts an aluminum sheet with a thickness of 0.2 millimeters; the separator adopts glass fiber; the positive electrode adopts the carbon cloth coated with CoFe2O4 / N-rGO or N-rGO or CoFe2O4 prepared above; the electrolyte adopts AlCl3 / EMIC ionic liquid, and the molar ratio of AlCl3 to EMIC is 1.3:1; the size specification: the negative electrode diameter is 14 millimeters, the separator diameter is 16 millimeters, and the positive electrode diameter is 12 millimeters. All battery assembly operations are carried out in an argon (Ar) filled glove box.

[0081] Battery test: The assembled batteries (Al-air batteries and Al-N2 batteries) were quickly transferred to a glass bottle filled with air (containing oxygen) or a nitrogen glove box. The battery performance test was performed on a LAND CT2001A multi-channel battery test system. The performance of the Al-air battery is shown in Figure 4 , and the performance of the Al-N2 battery is shown in Figure 5 . The following conclusions can be drawn from Figure 4 and Figure 5 .

[0082] 1. The positive electrode catalyst CoFe2O4 / N-rGO prepared in the embodiment of the present application can significantly reduce the overpotential of the Al-air battery and improve the energy conversion efficiency: as shown in the accompanying Figure 4 , in the Al-air battery test, the voltage hysteresis (i.e. overpotential) of the charge-discharge curve of the CoFe2O4 / N-rGO used in the embodiment of the present application as the positive electrode catalyst is significantly smaller than that of N-rGO and CoFe2O4 alone. This indicates that CoFe2O4 / N-rGO can effectively accelerate the kinetics of ORR / OER, thereby reducing energy loss during charging and discharging and significantly improving the energy conversion efficiency of the battery.

[0083] 2. The positive electrode catalyst CoFe2O4 / N-rGO prepared in the embodiment of the present application can significantly prolong the cycle life of the Al-air battery: Figure 4 The test results show that CoFe2O4 / N-rGO realizes stable cycling for up to 45 hours in the Al-air battery. This indicates that the positive electrode catalyst CoFe2O4 / N-rGO prepared in the embodiment of the present application significantly enhances the stability and durability of the positive electrode, effectively overcoming the shortcomings of poor stability of the positive electrode of existing Al-air batteries.

[0084] 3. The positive electrode catalyst CoFe2O4 / N-rGO prepared in the embodiment of the present application can significantly prolong the cycle life of the Al-N2 battery and improve the stability of the catalyst: as shown in the accompanying Figure 5 , in the Al-N2 battery test, CoFe2O4 / N-rGO exhibits excellent long-term stability with a cycle life of up to 120 hours; this is a great improvement compared with N-rGO alone (about 40 hours) and CoFe2O4 alone (about 90 hours). This effect directly solves the key challenge of the instability of the cathode electrocatalyst in existing Al-N2 batteries, which leads to a significant decline in overall performance.

[0085] 4, The positive electrode catalyst CoFe2O4 / N-rGO prepared in the embodiment of the application can realize high efficiency and multifunctionality of the battery system: the positive electrode catalyst CoFe2O4 / N-rGO prepared in the embodiment of the application simultaneously shows excellent performance in aluminum-air batteries and aluminum-nitrogen batteries, which proves the multifunctionality in energy storage and simultaneous chemical production (ammonia synthesis), and provides a solid foundation for developing the next generation of high-performance and multi-purpose aluminum-based battery systems.

[0086] The above is based on the ideal embodiment of the application, and the above description can be changed and modified by relevant personnel without deviating from the technical idea of the application. The technical scope of the application is not limited to the content of the specification.

Claims

1. A metal-gas cell comprising a negative electrode and an electrolyte, characterized in that, The metal gas battery is an aluminum-nitrogen gas battery; the negative electrode is aluminum; the preparation method of the positive electrode catalyst comprises the following steps: Disperse graphene oxide in a first solvent to obtain a graphene oxide solution; Add melamine and formaldehyde into the graphene oxide solution to perform a hydrothermal reaction to obtain a nitrogen-doped graphene oxide intermediate; Perform pyrolysis treatment on the nitrogen-doped graphene oxide intermediate to obtain three-dimensional nitrogen-doped graphene; Dissolve an inorganic iron salt, an inorganic cobalt salt and sodium hydroxide in a second solvent, and then add ethylenediamine to obtain a mixed solution; Disperse the three-dimensional nitrogen-doped graphene in the mixed solution, and perform a reaction at a temperature of 105-115 DEG C to obtain a three-dimensional nitrogen-doped graphene loaded cobalt ferrite CoFe2O4 / N-rGO positive electrode catalyst.

2. The metal-gas cell of claim 1, wherein The mass ratio of the graphene oxide to the melamine is (0.1-0.3):(0.4-0.6); the mass-volume ratio of the graphene oxide to the first solvent is (0.1-0.3) g:30 mL; and the volume ratio of the formaldehyde to the first solvent is (1-1.5):

30.

3. The metal-gas cell of claim 1, wherein The temperature of the hydrothermal reaction is 170-190 DEG C.

4. The metal-gas cell of claim 1, wherein The temperature of the pyrolysis treatment is 750-850 DEG C.

5. The metal-gas cell of claim 1, wherein The molar ratio of the inorganic iron salt, the inorganic cobalt salt and sodium hydroxide is (2-4):(1-2):(12-18); the molar-volume ratio of the inorganic iron salt to the second solvent is (2-4) mol:7 mL; the volume ratio of the ethylenediamine to the second solvent is (1.5-2.5):1; and the mass-volume ratio of the three-dimensional nitrogen-doped graphene to the second solvent is (0.01-0.1) g:7 mL.

6. The metal-gas cell of claim 1, wherein, The electrolyte is an ion liquid of aluminum chloride and 1-ethyl-3-methylimidazole chloride; and the positive electrode catalyst is coated on carbon cloth.

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